基于树状分叉裂缝网络的致密气藏压裂水平井产能预测模型

Productivity Model Considering Tree-shaped Fracture Characteristics for Fractured Horizontal Wells in Tight Gas Reservoirs

致密气藏压裂水平井产能预测时常常将裂缝简化为直线状裂缝,而实际地层中裂缝形态一般较为复杂,因而导致其产能预测的准确性受到一定程度的影响。基于更符合实际复杂裂缝形态的树状分叉裂缝网络,考虑了裂缝的形态特征及气体的滑动效应,建立了压裂水平井产能预测的新模型,并进行了产能的敏感性分析。计算结果表明,相比于直线状裂缝模型,树状分叉裂缝模型给出的水平井产能要高,其与树状分叉裂缝长度分形系数和分叉级数正相关,与分形角度负相关,与宽度分形系数几乎无关。此外,水平井产能随努森数和泄压半径增大而减小,随裂缝间距和长度的增大而增大,受裂缝渗透率的影响较小;裂缝产能与裂缝间距正相关,与裂缝渗透率几乎无关;然而裂缝长度的增加仅使两端裂缝的产能增加,中间裂缝的产能却有所减小。研究结果对致密气藏压裂水平井的设计和开发具有一定的指导意义。

In fractured tight gas reservoirs,hydraulically induced fractures are usually simplified into straight-shaped fractures for predicting productivity of horizontal wells.Whereas,actual fractures are so complex that accurate prediction productivity becomes challenging work.In this case,considering tree-shaped fractures better fitting with actual fractures and gas slippage effect,a new productivity model was proposed for fractured horizontal well and the contributing factors was examined to productivity.The results demonstrate that in comparison with the straight-shaped fracture,the present model in terms of the tree-shaped fracture predicts higher productivity which is positively associated with its length ratio and branching level whereas negatively correlated with its branching angle and almost unaffected by its width ratio.Furthermore,well productivity decreases with the Knudsen number and boundary radius of reservoir,whereas increases with the fracture spacing and length and is almost unaffected by the fracture permeability.Fracture productivity is positively associated with its spacing and unrelated to its permeability.While,increasing fracture length can increase fracture productivity in the toe and foot ends of horizontal well whereas decrease fracture productivity in the center.These findings contributes to design and development of horizontal wells in tight gas reservoirs.